The present invention generally relates to an optical information recording and reproducing apparatus for recording and reproducing information on an optical disk having optically detectable guide tracks and more particularly, to an optical information recording and reproducing apparatus in which a processing for recovering data errors at the time of reproduction of signals recorded on the optical disk is performed.
In optical disks having enormous potentialities as a memory having high density and large capacity, error control (error detection and correction) technique is vital in order to overcome error rate higher than those of magnetic recording apparatuses. Generally, optically detectable guide tracks such as guide grooves are provided in the optical disks so as to raise guide track density. A laser beam condensed to a diameter of about 1 .mu.m is irradiated over a recording layer formed on the guide track such that information signals are recorded on the recording layer by perforation, deformation of shape of the guide pit, change of optical reflectance of the recording layer, magnetooptical recording, etc.
Since recording pits and track pitch are formed on the order of microns, the optical disks are apt to incur various defects, dust and damage during their production processes or in environment for their use, thereby resulting in drop-out of reproduction signals. As a result, it is said that raw error rate of the optical disks ranges from 10.sup.-4 to 10.sup.-6 which is quite higher than that of 10.sup.-9 to 10.sup.-12 obtained in magnetic disks representative of known recording mediums.
Therefore, optical information recording and reproducing apparatuses employing optical disks have powerful error control and a verification function that immediately after data has been recorded at a track, contents recorded at the track are reproduced such that it is verified whether the data has been recorded at the track correctly. By using this verification function, verification is performed at the time of recording of the data. If it is found that the data is recorded at a defective sector referred to above and thus, contents of the data cannot be guaranteed, the data is rerecorded at an alternative sector provided at another location preliminarily.
Furthermore, in information recording and reproducing apparatuses including the optical information recording and reproducing apparatuses, in case an error has been detected at the time of read-out of the data, rereading of the target data is generally attempted as a error recovery processing.
With reference to FIG. 5 showing a reproduction signal processing circuit in the known information recording and reproducing apparatus, one example of an error recovery processing performed in the case where an error has been detected at the time of read-out of the data in the known information recording and reproducing apparatus is described. In FIG. 5, the prior art reproduction signal processing circuit includes an optical disk 1, a motor 2 for rotating the optical disk 1, an optical head 3 which condenses to a light beam having a diameter of about 1 .mu.m, a laser beam emitted from a semiconductor laser or the like so as to irradiate the light beam over the optical disk 1 and a laser drive circuit 4 for modulating and driving the semiconductor laser, etc. in response to a recording information signal inputted to a terminal A. The known reproduction signal processing circuit further includes a pre-amplifier 42 for amplifying weak signals from the optical disk 1, a frequency characteristics correcting circuit 43 for emphasizing a specific frequency so as to facilitate reading of the data, a differentiating circuit 7, an amplifier 8, a zero-cross comparator 9, an AND gate 15, a phase locked loop (PLL) circuit 46, an address/data reading circuit 16 and a microprocessor 63 for controlling recording signals and reproduction signals or controlling the known information recording and reproducing apparatus as a whole. In addition, the known reproduction signal processing circuit includes first and second envelope detecting circuits 44 and 12 for detecting an envelope of a signal, first and second comparators 11 and 14 and a bias setting circuit 45 for setting a bias of the second comparator 14.
Operation of the prior art reproduction signal processing circuit of the above described arrangement is described briefly, hereinbelow. A reproduction signal read by the optical head 3 is amplified by the pre-amplifier 42. Frequency characteristics of the reproduction signal amplified by the pre-amplifier 42 are corrected by the frequency characteristics correcting circuit 43. FIG. 7(a) shows one example of an output signal of the frequency characteristics correcting circuit 43. Peak detection of the reproduction signal is performed by two circuitries. One of the circuitries is a system for detecting peak of the reproduction signal and is constituted by the differentiating circuit 7, the amplifier 8 and the zero-cross comparator 9. An output signal of the differentiating circuit 7 is shown in FIG. 7(b), while an output signal of the zero-cross comparator 9 is shown in FIG. 7(c) such that data is carried at a rise edge of the output signal of the zero-cross comparator 9. A crossed portion in FIG. 7(c) represents a noise signal.
The other of the circuitry is a data gate detecting system for eliminating the noise signal referred to above and is constituted by the first envelope detecting circuit 44 and the first comparator 11. As indicated by the portion a in FIG. 7(a), an output signal of the first envelope detecting circuit 44 is usually set such that about 40% of amplitude of the input signal is clipped. Thus, an output signal of the first comparator 11 is obtained as shown in FIG. 7(d) and peak of the data is detected by logical product of FIGS. 7(c) and 7(d) as shown in FIG. 7(e).
Furthermore, output of the data is performed by a gate signal of a data detecting circuit for detecting presence and absence of the data such that the data is outputted to only a sector which is regarded as recording the data therein. The data detecting circuit is formed by the second envelope detecting circuit 12, the bias setting circuit 45 and the second comparator 14. An output of the second comparator 14 is obtained as shown in FIG. 7(f) and finally, an output of the AND gate 15 is obtained as the reproduction signal as shown in FIG. 7(g). In case this binary signal is read by the address/data reading circuit 16 and any error is detected by the address/data reading circuit 16 during or after reading of the data, the address/data reading circuit 16 feeds error information back to the microprocessor 63.
FIG. 6 is a flow chart showing processing at the time of read-out of the data in the known information recording and reproducing apparatus. In case the data can be correctly read by a single read-out, the program flow proceeds in the sequence of steps S19, step S47, step S22, step S23 and step S24. At step S19, a data read-out command is received, while at step S47, a retry counter RC is initialized. At step S22, the data is read out, while at step S23, it is judged whether or not an error has been detected. Finally, the program flow ends at step S24.
Meanwhile, in case the data is read by several read-outs, the program flow proceeds in the sequence of steps S19, S47, S22, S23, S48, S26, S22, S23, S48, S26, ---, S48, S26, S22, S23 and S24. At step S48, an increment is imparted to count of the retry counter RC. At step S26, it is judged whether or not the count of the retry counter RC has exceeded a retry number N.
In the known information recording and reproducing apparatus, if the remainder of previously recorded signals (referred to as "unerased signals", hereinbelow) as shown by the broken line in FIG. 8(a) is caused to overlap a new signal to which the data is updated in the same sector, such a phenomenon may happen that even if the data can be correctly read by verification of one optical disk drive, an error is produced in each read-out in another optical disk drive due to scatter in production quality such as scatter of the light beam produced by the optical system and the semiconductor laser, etc. as described briefly, hereinbelow. FIG. 8(a) shows an output signal of the frequency characteristics correcting circuit 43 of FIG. 5. Character a in FIG. 8(a) shows an output signal of the first envelope detecting circuit 44, while FIG. 8(d) shows a gate signal for detecting peak. FIG. 8(b) shows an output signal of the differentiating circuit 7, while FIG. 8(c) shows an output signal of the zero-cross comparator 9. Accordingly, peak of the data is detected by logical product of FIGS. 8(c) and 8(d) and thus, a portion of the unerased signals is detected erroneously as shown in FIG. 8(e). A gate signal. for detecting presence and absence of the data is shown in FIG. 8(f), while an output signal of the AND gate 15 also has a portion of the unerased signals as shown in FIG. 8(g). In this case, a data error is produced.
In case the data error is produced even if rereading is performed many times, the routine of steps S22, S23, S48 and S26 is repeated a predetermined reading number of N times after the processing of steps S19 and S47 and then, step S27 follows. As described above, such a case may take place that data in a sector having, e.g., many unerased signals is correctly read by verification of one optical disk drive but is detected by another optical disk drive as containing a data error.